1. Field of the Invention
The present invention relates to an implement driven by an internal combustion engine, such as an impact device, in particular a drilling or breaking hammer, a tamper, or some other device in which the operator must cause a force to act in a defined direction. In addition, the present invention relates to an operating method for such an implement.
2. Description of the Related Art
Impact devices often have a gasoline-powered internal combustion engine that drives an impact mechanism. The impact effect is transmitted to a corresponding tool in order to achieve the desired operational effect. Impact devices are predominantly used in two rotational speed ranges; a distinction is made between no-load operation and full-load operation. Full-load operation corresponds to the operating mode in which the device operates in the intended manner.
The operating mode of the internal combustion engine, and thus the distinction between no-load and full-load operation, can be selected by the operator using a gas lever housed in a handle. As long as the impact device is relieved of load, and in particular the impact mechanism is no longer loaded, for example during the displacement or lifting of the impact device from the soil, the gas lever often remains in the full-load position, because the operator continues to hold it pressed down. The throttle valve then remains fully open. In this operating state, only a slight power loss is taken from the engine. To the extent that no control measures are implemented, the engine would rotate up to its maximum rotational speed, which ultimately would be limited only by the gas dynamic behavior inside the engine. However, the achieving of the maximum rotational speed causes a reduction in the lifespan of the engine, the coupling, and the driven parts, as well as high vibrational loading and excessive noise. For this reason, it is known to limit the rotational speed using the ignition. Above the nominal rotational speed (operating rotational speed), the ignition time is displaced in the direction of a delayed ignition. If this displacement is not sufficient, the ignition is discontinued at least for some cycles. This function is stored in a characteristic curve in the ignition, and is used to limit the rotational speed.
In particular when there is a discontinuation of the ignition during individual operating cycles, uncombusted fuel is discharged to the environment through the exhaust. If, due to exhaust gas regulations, a catalytic converter is provided in the exhaust system, the uncombusted fuel collects in the catalytic converter, which can cause overheating of the catalytic converter and ultimately its destruction.